The ZX Spectrum +3 was released on the 16th of May 1987. It is a significant redesign from the original "Toastrack" 128K and Grey +2 models, with additional memory paging capabilities to support CP/M and additional ROM containing the +3DOS disc operating system code.
The "Black +2" appeared soon after. This computer can be one of two machines, a +2A or the later +2B. The lower case moulding carries one of these two designations, however this has been found not to be an accurate indication of which model the computer is as the majority of machines carrying the +2A label actually contain a +2B motherboard.
Development of the +2B continued until 1990. This was the last official model of ZX Spectrum produced.

+3 specific hardware

Black +2 specific hardware

Cassette interface daughterboard.

"Datacorder" cassette mechanism.

Timings and Contention

The contention and ram timings on the +3 and Black +2 differ significantly from earlier models due to the redesigned gate array. Timing patterns and memory contention are described in detail in the contended memory article.

Paging

The memory space is divided into four 16k pages and can be used in two ways; "Standard paging mode" and "Special paging mode".
Paging is controlled by performing I/O writes to ports 0x1ffd and 0x7ffd.

The bits are described in the table below:

Port

Bit

7

6

5

4

3

2

1

0

0x1ffd

Printer Strobe

Disk Motor

ROM high

0

Special paging

1

0x7ffd

Disable Paging

ROM low

Active Screen

RAM Bank

Standard paging mode

The 64k of ROM and 128k of RAM can be paged into the memory space as shown in the diagram below:

0xFFFF -0xC000

Bank 0

Bank 1

Bank 2

Bank 3

Bank 4

Bank 5(screen 0)

Bank 6

Bank 7 (screen 1)

0xBFFF -0x8000

Bank 2

0x7FFF -0x4000

Bank 5

0x3FFF -0x0000

ROM 0

ROM 1

ROM 2

ROM 3

Special paging mode

In special paging mode all four pages contain RAM. There are four combinations as shown in the diagram below: